Catheters of various types and sizes have been used by physicians extensively. One use of the catheter is in providing regional anesthesia which produces profound analgesia with minimal physiologic alterations. When used at the start of an operation, regional anesthesia minimizes the total dosage of inhalation or intravenous anesthetic drugs required, hastens awakening, and permits early ambulation. When administered at the conclusion of surgery, regional anaesthesia produces post-operative analgesia with reduced risk of respiratory depression. Furthermore, certain types of pain are difficult to treat with systemic narcotics. For example, a bladder spasm following genitourinary surgery may be exacerbated by systemic opioids but is easily treated with a caudal epidural block. When prolonged analgesia is required, a catheter is inserted into the caudal or lumbar epidural space to provide intermittent or continuous injections of local anesthetics.
Caudal epidural anesthesia is notable for its simplicity, safety, and effectiveness and is one of the most frequently used regional anesthetic techniques for operations below the diaphragm in children.
When continuous pain relief is desired, the only equipment presently available is either a 19 or 20 gauge epidural catheter which is passed through either a 17 gauge Tuohy or an 18 gauge Crawford needle. Designed specifically for adults, these needles are approximately 31/2" long and have an outside diameter ranging from 0.050" to 0.059" along with an inside diameter ranging from 0.33" to 0.041". However, these needles are extraordinarily cumbersome to use in children, since the distance from the skin to the epidural space is only 10-15 mm. Obviously, smaller needles and catheters are desirable.
Continuous lumbar epidural anesthesia is a well-established and accepted technique in adult patients. It differs from caudal epidural anesthesia by the location where the needle is inserted. A lumbar approach has several advantages over the caudal epidural technique. However, the lumbar approach has more problems as well. First, placement of a lumbar epidural needle is technically more difficult than placing a needle into the caudal epidural space, particularly with the 17 and 18 gauge equipment presently available for use. Second, there is a greater risk of unintentionally puncturing the dura. This is commonly known as an unintentional spinal tap with the possibility of severe headaches depending on the size of the dural puncture hole. The smaller the hole, the less likely a headache. Obviously, a 17 or 18 gauge hole in the dura is much more likely to cause a severe headache than a 22 or 23 gauge puncture hole.
The smallest presently offered epidural catheter is a 20 gauge continuous epidural catheter with an outside diameter of approximately 0.035". This catheter is constructed of a spring wire guide coated with a plastic material. The distal end of the spring wire guide appears to have been stretched to allow the plastic material to form in between the stretched windings. This catheter is advertised as kink-resistant, but is still kinkable particularly when a patient would bend or collapse the catheter by laying on or twisting the body of the catheter outside the insertion site.
Since the plastic material is coated over the spring wire guide, the coating appears to have fluid pressure limitations as well as being susceptible to being easily ruptured.
Another problem associated with the distal end of the catheter is that of tissue ingrowth. Here, tissue is allowed to grow within or between the winding coils of the distal tip. The elastic distal spring tip is also susceptible to uncoiling when the catheter is removed from the patient. This causes trauma to the insertion site as well as possible injury to the dura.